Internet sites like Wikipedia are controversial, because anyone is able to edit the information on their site. Most information might be correct, while others times it might not, due to trolls or just lack of knowledge in the topic
The main reason why sites like Wikipedia are considered controversial research sources is that everyone has access to them. Therefore, a person does not need to prove his knowledge or expertise before he writes something. This means that the information presented could potentially be wrong, biased or incomplete. When you are researching a topic, you need to make sure that all the statements you include are factually correct, and that if something is an opinion, you state so and reference it properly.
